The Sdudy On The Purification Characteristics Of Flux And Its Application On A356 Aluminum Chips Recycling

With the excellent casting performance and mechanical properties,A356 aluminum alloys are widely used in commumication,construction,automobile and other industrial fields.Large amounts of aluminum chips were produced in the machining processes of A356 material parts.Research on the purification flux and process for A3 56 aluminum chips recycling has remarkable economic benefits and environmental values.Purify the aluminum melt which was involved lots of inclusions with flux has the advantages of good purification effect,low cost,simple operation,etc.The studies on flux purification almost focusing on the optimization of purification process,but less concern about the thermodynamic and kinetic processes and the interaction between flux,aluminum melt and Al2O3 during the purification process.The effect of alkali metal fluorides on flux melting point,the interfacial tension between flux and A356 aluminum alloy,interfacial tension between flux and Al2O3,the coalescence behavior of aluminum chips in molten flux and it's mechanism were researched by differential thermal analysis(DTA),optical microscopy(OM),X-ray diffractometer(XRD),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),electron-tensile tester,to provide guidance on the design of efficient purification flux.Orthogonal experiment was used to optimize the flux composition and purification processe for the recycling of A356 aluminum chips.The additions of NaF,KF to equalmolar NaCl-KCl decreased the melting point of flux significantly.The melting point decreased by 6.68%and 7%respectively when the flux containing 5%NaF,5%KF.Na3AlF6,AlF3 decreased the melting point modestly.MgF2,BaF2,SrF2 had little influence on the melting point of flux.CaF2 increased the melting point slightly.The interfacial tension between equalmolar NaCl-KCl and A356 aluminum alloy was 735mN/m at 740 ?.The interfacial tension decreased significantly with increasing NaF,KF content.The additions of 15%NaF,15%KF decreased the interfacial tension to 372.27mN/m and 354.23mN/m respectively.The interfacial tensions were decreased by the additions of Na3AlF6,MgF2,BaF2,SrF2,CaF2 and the minimum values were reached when the content of each of these fluorides was 5%.The interfacial tension increased with the addition of AIF3.The reason that interfacial tension decreased for fluoride addition could be explained in terms of enrichment of surface active elements Na,K in the interface of flux and A356.The interfacial tension between flux and Al2O3 decreased significantly when AIF3 was added to equalmolar NaCl-KCI.NaF,KF increased the interfacial tension.BaF2,SrF2 increased the interfacial tension slightly,Na3AlF6,MgF2,CaF2 almost had no influence on interfacial tension.A356 aluminum chips could not coalesce in equalmolar NaCl-KCl at 740?.NaF,KF,Na3AlF6 additions to NaCl-KCl salt respectively promoted coalescence significantly.The coalescence ability of flux with additions of AlF3,CaF2,BaF2,SrF2 was good.MgF2 had poorest coalescence ability among all fluorides.The coalescence process of aluminum chips in molten flux was:Oxide film was destroyed by thermal stress and the corrosion of F-ions;The destroyed oxide film was striped into flux by interfacial stress;Direct contaction of aluminum and aluminum between adjacent aluminum chips were produced and they coalesced into large-size liquid aluminum drops driven by the minimized interfacial energy.Three compositions of fluxs were designed based on the physical and chemical characteristics of flux,the interaction specificities of flux with molten A356 aluminum and Al2O3.Flux composition and purification process were optimized by orthogonal experiment,the results showed that the best flux component was 85%(NaCl-KCl)+8.5%Na3AlF3+4.5%AlF3+2%CaF2,the most effective flux addition method was that adding aluminum melt with well mixed flux and aluminum chips,the most suitable flux content was 1%.With the optimized purification process,the tensile strength of as-cast of A356 with 30%aluminum chips addition reached 189MPa,increased by 31.6%coMPared with the sample that hadn't been purified,the degassing rate was 80.4%.